Rapid venom evolution in pit vipers may be defensive

July 18, 2011, American Museum of Natural History

Research published recently in PLoS One delivers new insight about rapid toxin evolution in venomous snakes: pitvipers such as rattlesnakes may be engaged in an arms race with opossums, a group of snake-eating American marsupials. Although some mammals have long been known to eat venomous snakes, this fact has not been factored into previous explanations for the rapid evolution of snake venom. Instead, snake venom is usually seen as a feeding, or trophic, adaptation. But new molecular research on snake-eating opossums by researchers affiliated with the American Museum of Natural History suggests that predators factor into the rapid evolution of snake venom.

"Snake venom toxins evolve incredibly rapidly," says Robert Voss, curator in the Department of Mammalogy at the American Museum of Natural History. "Most herpetologists interpret this as evidence that venom in snakes evolves because of interactions with their prey, but if that were true you would see equally rapid evolution in toxin-targeted molecules of prey species, which has not yet been seen. What we've found is that a venom-targeted protein is evolving rapidly in mammals that eat snakes. That suggests that venom has a defensive as well as a trophic role."

Several groups of mammals are known for their ability to eat venomous snakes, including hedgehogs, mongooses, and some opossums. Opossums, which belong to the marsupial family Didelphidae, consist of about one hundred known and several dozen undescribed species. Most of these opossums live in Central and South America, although there is one representative in the north that is familiar to those who spend time outside at night: the Virginia opossum.

Some didelphids, including the Virginia opossum, are known to eat rattlesnakes, copperheads, and some species of tropical pitvipers known as lanceheads. All of these pitvipers have venom containing dozens of highly toxic compounds, including many that attack blood proteins, causing massive internal hemorrhaging in nonresistant warm-blooded prey species, mainly rodents and birds.

The new research came out of a previous phylogenetic study of marsupials, published as a Bulletin of the American Museum of Natural History, that suggested unusually rapid evolution in one gene among a group of snake-eating opossums. The rapidly evolving gene codes for von Willebrand's factor, an important blood-clotting protein that is known to be the target of several snake-venom toxins. The association of rapid evolution in a venom-targeted gene among just those opossums known to eat pitvipers was the essential clue that prompted further study.

"This finding took us by surprise," says Sharon Jansa, associate professor in the Department of Ecology, Evolution and Behavior at the University of Minnesota and a Museum research associate. "We sequenced several genesincluding the one that codes for von Willebrand Factor (vWF)to use in a study of opossum phylogeny. Once we started to analyze the data, vWF was a real outlier. It was evolving much more rapidly than expected in a group of opossums that also, as it turns out, are resistant to pitviper venom."

The recently published research demonstrates that the rate of replacement substitutions (nucleotide changes that result in amino-acid changes) is much higher than the rate of silent substitutions (nucleotide changes that have no effect on the protein) in the von Willebrand Factor gene among pitviper-eating opossums. Typically, high rates of replacement substitutions means that the gene is under strong, sustained natural selection. That only happens in a few evolutionary circumstances.

"Most nucleotide substitutions have little or no effect on protein function, but that doesn't seem to be the case with vWF in these venom-resistant opossums," says Jansa. "The specific amino acids in vWF that interact with toxin proteins show unexpectedly high rates of replacement substitutions. These substitutions undoubtedly affect protein function, suggesting that the vWF protein can no longer be attacked by these snake toxins."

"It is so uncommon to find genes under strong positive selection, that the exceptions are really interesting and often conform to one evolutionary circumstance when two organisms are coevolving with each other," says Voss. "We've known for years that venom genes evolve rapidly in snakes, but the partner in this arms race was unknown until now. Opossums eat snakes because they can."

Related Stories

Venoms from different snake families may have many deadly ingredients in common, more than was previously thought. A study published in the online open access journal BMC Molecular Biology has unexpectedly discovered three-finger ...

Axel Barlow's paper in Proceedings of the Royal Society B on saw-scaled vipers shows that snakes which have evolved to feed on scorpions have also evolved venom which is more lethal to scorpions, demonstrating that changes ...

Many people worry about the manner of their death. Death by car accident, death by cancer and death by gunshot are some of the more dreaded ways to go. No less awful is the prospect of death by snakebite. So a new research ...

The dreaded Matabuey, a snake so fearsome its name means "ox killer," has a deadly bite that immobilizes its prey in minutes, making it the kind of creature generally to be avoided. But far from steering clear of the legless ...

While studying a way to more safely and effectively collect snake venom, University of Florida researchers have noticed the venom delivered by an isolated population of Florida cottonmouth snakes may be changing in response ...

For several decades, snake venoms have been used in pharmacology to make new drugs. But a French team of pharmacologists, clinicians, systematists and conservation biologists, headed by Nicolas Vidal of the Laboratory Systématique, ...

Researchers at Duke University have created a framework for helping bioengineers determine when to use multiple lines of cells to manufacture a product. The work could help a variety of industries that use bacteria to produce ...

A team of researchers with the University of Tübingen in Germany has found an example of a fish that is able to control light reflected from organs next to its pupils—a form of photolocation. In their paper published in ...

How many generations of snakes does it take so that the "naturally selected" or surviving snakes' venom is effective again to kill their enemies? I doubt that's really the way a rapidly-changing venom is created. And I don't mean the "Creator" either. I have a suspicion that we know too little about the consciousness of animals, by the fact of how little we know about our own. I'm suggesting that animals , by way of consciousness, can alter and shape their physical needs over a much shorter time than has previously been thought. These changes aren't consciously made, but I've always thought that DNA itself has consciousness that can affect changes required for survival, the most powerful force of life.

I'm suggesting that animals , by way of consciousness, can alter and shape their physical needs over a much shorter time than has previously been thought. These changes aren't consciously made, but I've always thought that DNA itself has consciousness that can affect changes required for survival, the most powerful force of life.

I am visualizing Lamarck in some other world ... I'm not sure if he's happy to realize that people are still hanging on to his ideas after all these centuries, or in despair over the fact that in all thattime nobody's come up with a better argument for them.

I wouldn't apply Lamarck's theory to my own, because there is a difference. He proposed that animals can change themselves like the giraffe's long neck by its constant stretching. I'm talking about a much more subtle force, that from a mechanistic scientist's perspective, can't acknowledge lest they be ostracized from their community of mechanistic colleagues. That kind of peer pressure can alter your experience despite what you see with your own two eyes. I've seen it happen many times, and it's the kind of denial that is impossible to overcome. There are forces at work in the life of a cell that are unfolding before our eyes, astounding and never-before-imagined. We have a very long way to go before knowing all of life's processes. A virus will inject its DNA into a cell to convert it to one of its own, isn't that beyond the action of just a dumb collection of nucleic material? Or the way a virus can lay low and reappear years later?

Scoff if you'd like, but the mind/body connection is undeniable and reams of new, valid information have been compiled in the past couple of decades. If brain signaling, a multi-tasking, highly sophisticated mechanism used by an organism to heal itself, trigger specific muscles, control involuntary functions, and so on, why couldn't it also signal and communicate with its own DNA,a soldier in the offensive/defensive strategies of survival?

why couldn't it also signal and communicate with its own DNA,a soldier in the offensive/defensive strategies of survival?

[sarcasm mode on]Yes, and the mind certainly can control quantum states of individual atoms in your body.[sarcasm mode off]

You have to take into account what the mind can do via electric impulses viz: Control over muscles, senory apparatus and glands (i.e. anything that is enervated via nerve cells).DNA does not fit that bill.

DNA certainly does fit the bill. Its ability to monitor its own accuracy, snip out mutations, and replace defective sections with exact matches of the original in repair mode billions of times a minute in the body is awe-inspiring. You think an organism is just a jumble of electrical connections that act like a man-made device? That device would take eons to build.

In a previous existence, I suggested I was serving a useful purpose by providing opportunities to those who like to argue over slender pretexts. I am pleased to see I am doing the same in my new existence.

The point was: How do neural impulses from the mind act on DNA? The DNA trepair mechanism is one (of many) autonomous mechnaisms working in the body (e.g. our immune system or the system that keeps our pH balance within acceptable limits)

Scoff if you'd like, but the mind/body connection is undeniable and reams of new, valid information have been compiled in the past couple of decades. If brain signaling, a multi-tasking, highly sophisticated mechanism used by an organism to heal itself, trigger specific muscles, control involuntary functions, and so on, why couldn't it also signal and communicate with its own DNA,a soldier in the offensive/defensive strategies of survival?

Have you talked to Deepak Chopra about this? I am sure he would be fascinated. But no doubt he would suggest adding in comments about quantum physics, too.

I am not ruling out that TK is taking the mickey. But that would make talking to Deepak C even more fun.

@Y8Q412VBZP21010: You remind me of a boy in an English boarding school, "mum doesn't come around very much"; smart and lonely. You don't make any real rebuttal, you just snipe and expect to hide behind the backs of others who share your predispositions.Make a scientific-based argument that disproves my assertions.

Eh? I was half-thinking you were joking. I found it hard to believe you were serious.

But it seems you aren't. If you're challenging me to give you a clue, I concede defeat as fast as I possibly can: "MISSION IMPOSSIBLE!"

If you do want to get refutations, I suggest you offer a $10,000 prize to anyone who can convince you that you're wrong. Admittedly, anyone with sense knows that really means: "I'll give away $10,000 before I'll admit that I'm wrong." Offer as big a prize as you like, your money is safe.

Eh? I was half-thinking you were joking. I found it hard to believe you were serious.

But it seems you aren't. If you're challenging me to give you a clue, I concede defeat as fast as I possibly can: "MISSION IMPOSSIBLE!"

If you do want to get refutations, I suggest you offer a $10,000 prize to anyone who can convince you that you're wrong. Admittedly, anyone with sense knows that really means: "I'll give away $10,000 before I'll admit that I'm wrong." Offer as big a prize as you like, your money is safe.

Another thing that I'm right about is that your histrionics are a weak attempt to weasel your way out of a direct challenge. You have nothing at all to say.

There is no such biological mechanism. Such a mechanism would require an instinctive knowledge of each and every codon in the DNA and how they interact to produce the phenotype.

Now there IS a mechanism for increasing the rate of mutation but there is no way to controll where the mutations occur. When an organism is under stress it produces various chemicals that can increase mutation rates. Mutations are random and not directed. The direction of evolution comes from the environment not some magical knowledge of how all the chemicals interact.

Another thing that I'm right about is that your histrionics are a weak attempt to weasel your way out of a direct challenge. You have nothing at all to say.